Princess Celestia stood on her room's balcony. her mane billowing slightly in the cool night breeze. Her eyes were closed, contemplating matter of the state that were buzzing around in her mind. In between every pressing matter, her concern drifted to the six ponies that had come to help her more than she would have ever expected: Twilight Sparkle, Applejack, Pinkie Pie, Rarity, Fluttershy and Rainbow Dash.

There was then knocking on her door. As Celestia turned her head around and beheld her sister's face, Luna, as she trotted in. Closing the door as she walked, Luna could see the troubled face of her sister. "What troubles you, Sister?" she asked in a matter-of-fact tone.

"Nothing that I can't handle, Luna," Celestia replied, walking up to her sister and stopping when they were face to face with each other.

However, before they could embrace each other, a sudden gust of wind blew into the room, and the air turned unnaturally warmer. Celestia whipped around, and Luna stepped up beside her sister. Before them stood a silver alicorn, a stallion of noble bearing but was wearing a grim look on his face. He nodded at one sister to the other in silent greetings.

Luna gasped, and while stunned for a brief moment, Celestia managed to recover her composure. "B-Braveheart," she greeted with a slight hesitation. "It has been long since we have last seen each other, and longer still since we last laid eyes on one another. How have you been?"

The silver alicorn's face softened, revealing a slight smile on his face. He began to speak with a rich voice, "My name has changed to Cosmo ever since I was chosen to be the Sentinel," he replied. "But yes, it is good to see you again, though I wish that it were under better circumstances."

"Well, I'll say!" spat Luna. "Where were you the night my sister and me were battling Discord?! You were nowhere to be seen, when we could have used the aid of any other alicorns!"

Cosmo approached the fuming princess, and met her steady gaze with one of his own. "Harmony exists in conjunction with Discord," he replied coolly. "Did you not think that my heart was pained when I heard that our believed birthplace was twisted as such? I would have endured a thousand deaths just to save it. The truth of the matter is more complicated than anypony care to realize. Am I right, Celestia?"

Luna looked up at her sister, who had been sporting a poker face in the conversation thus far. "What are you waiting for, Sister?" Luna asked, her tone sharp with her palpable anger. "Why do you remain silent, even when you know the truth behind my words?"

Cosmo chuckled, shaking his head in amusement. He shot Luna look of incredulity. "Are you really that thick, dear Luna?" he asked mockingly. "You cannot even see what your sister has done thus far?"

Luna recoiled in surprise, but cast it aside just as quickly. "She defended the land from Discord!" she spat. "She changed Equestria for the better! There is so much more happiness in this place thanks to her! You could not say the same!"

This time, Cosmo burst out laughing, which added to the rage that was already building up inside Luna. Nopony would mock her sister as such and get away with.

"Nopony but the Sentinel, that is," Cosmo chided. Luna gaped at him. How had he known what I was thinking?

"Its my duty what happens in everypony's daily lives, sweet little Luna," he explained. "I know what the two guards outside of this place are thinking about right now. I know what dear Twilight Sparkle, and even her friends are dreaming about right now. I know so much that is happening at this current time. There is only one thing I cannot read, and that happens to be the mind of your dear sister." He moved his attention to the still silent alicorn. "That...is something which disturbs me as the Sentinel. Do you know the truth of why I'm here, Luna?"

Luna backed away from her sister, unconsciously placing herself next to Cosmo. She tried to look her sister in her eye, but could not make contact because of the shadows blocking them. "Sister," she asked softly. "None of this makes sense, and it does not help that you remain silent. Please, say something."

"Oh, she won't," went Cosmo. "If I know her well enough, she will keep her silence, so I'll spin you a tale instead. When your sister went up against Discord, she would have known that the elements of Harmony, no matter how powerful the tales say they were, could not possibly have defeated Discord. As I said, Harmony exists to provide balance to the chaos the Discord would sow. Instead, she chose to infuse the elements with the essences of six different alicorns, who at the time embodied an element each. The fact of the matter is that she did not reveal this to anypony else."

Luna stared at her sister, her mouth agape. "Tell me... Tell me that this isn't true, Sister," she pleaded.

"Oh, there's more," Cosmo interrupted. "When she managed to defeat Discord, she caused a change in the fundamentals of the world. Weather no longer worked on its own, and even the lands no longer matured at their own whims. Instead, now earth ponies care for the land and the pegasi move the weather as and when needed."

Luna retreated a few more steps away from her sister, a complete opposite of Cosmo who was now standing right behind Celestia. Celestia was still silent, and her face still concealed her eyes.

Cosmo was still continuing his list of arguments. "Ponies now live in a time of order, yes, but at what cost? Two rulers lead them from this very castle, the elder of which has stripped them of their true and free will, maintaining the illusion that the ponies actually have such a thing." Cosmo disappeared in a flash of grey, and rematerialized beside Luna, who shied away from his presence. "Let's not forget, dear Luna, that she banished you, one the of the last remaining alicorns to the moon. True, you had changed for the worse, but that's why there is always a Sentinel. We have to guide events in the right flow, and the one that no longer exists in this plan is your sister, dearest Celestia. These are the violations that you are hereby found to have made. What say you in your defense?"

Luna stepped in front of Cosmo, her cheeks wet with tears. "Please," she sobbed. "I beg you, stop all of this. Celestia would never do harm anypony. Even sending me to the moon was a merciful act, so please. I beseech you to let this go."

"Luna, step aside," Cosmo said in a serious tone.

"What?" Luna asked, still sobbing. She looked at Cosmo, who hid his eyes from her. She never got her answer, for she was suddenly moved to the far wall by magic.

She looked up, and saw Cosmo block a magic bolt from Celestia, easily flicking it aside as if it was nothing. The door to the room burst open, but a grey aura enveloped it and it closed just as quickly, turning into heavy metal as it slammed shut. Luna returned her focus to the dueling alicorns, and saw Cosmo's own magic bolt that nicked Celestia on her face.

"Celestia, have you lost all sense?!" Cosmo fumed. "Cease this at once, and face your judgement!"

Celestia did not reply to his statement. Instead, her horn began to build up with magical energy, and Cosmo attempted to blast her with yet another bolt, which sailed right past her.

Celestia finished her spell and cast it, binding her opponent in place. "You should never have come here, old friend," Celestia said, her tone almost maniacal. She lifted her head, and her face was contorted with what appeared to be madness. "I'll make sure that you're the last Sentinel to live, just like I took care of the other alicorns."

"And you never learn to respect your betters!" Cosmo spat. With a glow of his horn, he was free to move again. With a flick his horn, he sent Celestia flying towards the roof of her chambers at a high speed.

Just before she hit the ceiling, Celestia managed to invert herself with magic. She glared mockingly at the silver alicorn before her, taunting him with a Tut-tut. Her horn glowed with magic, and everything in the room that was not a pony or an animal flew towards Cosmo.

Cosmo closed his eyes, channeling magic through his entire being. When his eyes opened, they glowed white, and everything in the room turned to ash, flying out the window as he looked that way. When the last bit flew out, his eyes returned to normal. He looked at Celestia, who was now almost directly above him. "When I realized that you were no longer part of the fundamental world, I did not expect your power to have increased so."

Celestia threw her head back and laughed, and made no attempt to address his remark. When she was done laughing, she gasped when she saw that the Sentinel was standing directly in front of her, his horn glowing with magic. Before she could even react, his horn came to rest upon her head, and she felt a thousand sensations die out as she lost her connection to the flow of magic.

Celestia crashed to the floor with a loud Thud!, a direct contrast to the graceful fall of the stallion next to her.

"I came here for a reason, Celestia," Cosmo snarled. "You will be judged for the crimes you have committed, especially resisting the judgement of the Sentinel. Based on the atrocities that you have committed, not even a ten millenniums in Tartarus would be sufficient."

A cough came from behind him, and Cosmo turned his head slightly. "You have something to add, Luna?"

Luna stepped up next to him, her eyes red from the tears that had been flowing as she saw what her sister had become. "Please, I beg of you," she sobbed, her voice almost cracked. "Please, show her leniency."

Cosmo turned his eyes back towards his captive, who was laughing and mumbling to herself. "I pity her, but in her condition she is a danger to all. I cannot even begin to think of a suitable means to hold her, that may also contain her redemption."

Luna cleared her throat, trying to regain her composure. She looked pleadingly into the male alicorn's eyes. "When all has been said and done, until the time when I am needed shall again come, I shall return to where my roots had begun."

Cosmo pondered the statement for a while, and smiled. Luna had given him the perfect idea on where to house the now deranged ruler of Equestria.